Communication method supervised by an interference classification

ABSTRACT

The present invention relates to a communication method supervised by an interference classification. For two couples of transmitting and receiving terminals having communications using the same radio resources and interfering with each other, a partition of the interference diagram into a plurality of distinct zones is determined, each zone corresponding to a particular processing. For an operating point of the transmitting and receiving terminals, the zone in which this point is located is determined, and the processing associated with that zone is performed in at least one of the receiving terminals.

TECHNICAL FIELD

The present invention generally relates to the field of wirelesstelecommunications systems and more particularly the reduction of theeffects of intra-band and intercellular interference in cellulartelecommunications systems.

BACKGROUND OF THE INVENTION

One of the problems affecting communication within a cellulartelecommunications system is that of the interference generated by othercommunications of the cell or neighboring cells. A distinction istraditionally made between intercellular interference due tocommunication from neighboring cells and intra-cellular interference dueto communications by the same cell where the terminal is located.

Many techniques have been proposed and implemented to reduceintra-cellular interference. Most of these techniques are based on anallocation of orthogonal transmission resources, for example timetransmission intervals (TDMA), frequency transmission intervals (FDMA),OFDM orthogonal frequency-division multiplexing intervals (OFDMA),transmission codes (CDMA), transmission bundles (SDMA), or even acombination of such resources, so as to separate the differentcommunications of a same cell.

Radio resources being rare, they are generally reused, at least in part,from one cell to the next. A radio resource management (RRM) module isthen responsible for statically or dynamically allocating the radioresources to the different cells. It is in particular known tostatically reuse radio frequencies following a bi-dimensional pattern(Frequency Reuse Pattern).

Due to the reuse of radio resources, a first communication between afirst terminal and a first base station of a cell can be interfered withby a second communication, using the same radio resource, between asecond terminal and a second base station of a neighboring cell. Thesituation is even more critical when the cells are adjacent and theterminals are on the cell border. In that case, the terminals musttransmit at full power and the interference level is then higher.

For a given communication, here called first communication, theinterference caused by a second communication using the same radioresource as the first is commonly called intra-band interference. Incontrast, interband interference is the interference caused by a secondcommunication using a distinct radio resource (for example a neighboringradio frequency or another radio interval) from that used by the first.

FIG. 1 shows a very simplified cellular telecommunications system,comprising two cells 151 and 152. The first cell 151 contains a firstcouple of terminals formed by a first transmitting terminal 110 and afirst receiving terminal 120. Similarly, the second cell 152 comprises asecond couple of terminals formed by a second transmitting terminal 130and a second receiving terminal 140. Terminal here refers to a mobileterminal or a base station, or even a relay terminal in the case of arelayed channel. In particular, it will be understood that here we areconsidering both uplink and downlink communications. It is also assumedthat the first communication between the terminals 110 and 120 uses thesame radio resource(s) as the second transmission between the terminals130 and 140 so that the two communications interfere with each other.

The processing and reduction of intercellular interference have been thesubject of considerable research.

The simplest processing method is to consider the interference as asimple thermal noise. This processing method is only acceptable,however, if the interference level is low. It should be noted that mostpower allocation algorithms are based on this hypothesis.

Other processing methods make it possible to reduce the interference byestimating the information signal of the interfering communication(s).This assumes that the considered receiving terminal knows how to decodethese information signals and consequently knows the codes having beenused to encode them. Known amongst these methods are in particular PIC(Parallel Interference Canceller) or serial (Successive InterferenceCanceller) interference reduction plans, well known by those skilled inthe art.

Another traditional approach for reducing the interference level is toimplement an adaptive power control method. Such a method makes itpossible to monitor the power levels of the different transmittingterminals so as to guarantee a predetermined service quality to thedifferent users. This service quality can be measured depending on thecase in terms of rate, latency, packet error rates, spatial coverage,etc. Traditionally, service quality metric refers to the parameter(s)used to measure it. As a general rule, a user's communication requires aminimum service quality that is taken into account or negotiated duringthe procedure to admit the user into the cell. This minimum servicequality is expressed in the form of a stress on the service qualitymetric: latency below a threshold, rate greater than a guaranteedminimum, etc. The power allocation is then done so as to comply with thestress on the service quality metric.

Lastly, the power allocation can be handled in a centralized manner(Centralized Power Allocation) by a specific network node, NC (NetworkController), or in a distributed manner (Distributed Power Allocation)within each terminal.

Reciprocally, for a given transmission power stress, it is possible toseek to maximize the rates of different users, to increase the spatialcoverage of different terminals, to reduce the latency for differentcommunications, in other words to increase the service quality fordifferent users. In this context, the service quality is expressed inthe form of a so-called utility function relative to one or more users.For example, this utility function can be the sum of the rates of thedifferent communications (Sum-Rate) or the minimum rate (Min-Rate) onthose communications.

The known methods for processing the inter-cellular intra-bandinterference are relatively inflexible in that they do not adapt to theinterference levels affecting the different communications.

A first problem at the base of the invention is consequently to proposea communication method for a wireless telecommunications system, inwhich the processing of the interference is adaptive as a function ofthe interference level.

Another problem at the base of the invention is to provide a powerallocation method or a method for maximizing a utility function thattakes this adaptive processing of the interference into account.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is defined by a communication method for acellular telecommunications system comprising at least one first coupleof terminals formed by a first transmitting terminal and a firstreceiving terminal and a second couple of terminals formed by a secondtransmitting terminal and a second receiving terminal, a firstcommunication between the terminals of the first couple using the sameradio resources as a second communication between the terminals of thesecond couple, such that the two communications interfere with eachother. According to this method:

-   -   the channel coefficients are estimated between said transmitting        terminals and said receiving terminals;    -   an interference diagram is deduced for at least the first        receiving terminal, the diagram being obtained for a first        transmission power range of the first transmitting terminal and        a second transmission power range of the second terminal, and        for at least one couple of rates for the first and second        communications;    -   for the considered couple of rates, a partition of the diagram        into different zones is determined, each zone corresponding to a        distinct type of processing of the interference for at least the        first communication;    -   a zone of the partition is selected containing an operating        point of the first and second receiving terminals;    -   at least in the first receiving terminal, the processing is done        for the interference corresponding to the zone thus selected.        Advantageously:

In the first type of processing, the interference is processed asthermal noise to decode said information signal of the firstcommunication.

In the second type of processing, the information signals of the firstand second communications are the subject of joint decoding.

In the third type of processing, the information signal of the secondsignal is decoded first, an estimate of the interference signal due tothe second communication is deduced therefrom and it is subtracted fromthe signal received by the first receiver, the information signal of thefirst communication being decoded from the signal thus obtained.

Said operating point can be obtained by minimizing the power allocatedto the first transmitting terminal for a given rate of the firstcommunication.

Alternatively, said operating point is obtained by joint minimization ofthe powers respectively allocated to the first and second transmittingterminals, under a stress pertaining to a first service quality metric.In particular, said operating point is obtained by joint minimization ofthe powers respectively allocated to the first and second transmittingterminals for given rates of the first and second communications.

A plurality of partitions can first be determined, said zone then beingobtained by selecting the one of said partitions maximizing, at theoperating point, a utility function depending on the rate of the firstcommunication.

Alternatively, a plurality of partitions is determined, said zone thenbeing obtained by selecting that of said partitions maximizing, at theoperating point, a utility function jointly depending on the respectiverates of the first and second communications. Said utility function canbe the sum of the rates of the first and second communications, or aminimum rate for the first and second communications.

In one embodiment, said communication system comprises a plurality ofcouples each formed by a transmitting terminal in communication with areceiving terminal and the couples are grouped together in pairs byselecting, for each first couple of terminals, a second couple ofterminals of said plurality generating the strongest interference levelon the communication between the terminals of the first couple, thefirst couple of terminals and the second couple of terminals thenconstituting a pair.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear upon readingone preferred embodiment of the invention, done in reference to theattached figures, in which:

20

FIG. 1 diagrammatically illustrates an inter-cellular, intra-bandinterference situation in a cellular communication system;

FIG. 2 diagrammatically illustrates a model of the cellularcommunication system of FIG. 1;

FIG. 3 diagrammatically illustrates a first interference diagram for afirst communication.

FIG. 4 diagrammatically illustrates a second interference diagram forthis same communication;

FIG. 5 diagrammatically shows an interference diagram for first andsecond communications;

FIG. 6 diagrammatically shows a flowchart of a communication accordingto one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

We hereafter consider a cellular communication system comprising aplurality of pairs of transmitting terminals and receiving terminals. Asbefore, we will assume that the different communications can be affectedby an intra-band interference. The wireless communication system can,for example, be a cellular communication system or an ad hoccommunication system.

To simplify the presentation, we will first look at the case of a systemhaving only two pairs of terminals, as illustrated in FIG. 1.

FIG. 2 shows a model of the telecommunications system of FIG. 1.

If x₁, x₂ respectively denote the signals sent by the transmittingterminals 210 and 230 and y₁, y₂ denote the signals respectivelyreceived by the receiving terminals 220 and 240, we have:

y ₁ =g ₁₁ x ₁ +g ₁₂ x ₂ +z ₁

y ₂ =g ₂₁ x ₁ +g ₂₂ x ₂ +z ₁   (1)

where z₁,z₂ are Gaussian white noise samples g₁₁,g₂₁ are the channelcoefficients between the transmitting terminal 210 and the receivingterminals 220 and 240, respectively, and g₂₂,g₁₂ are the channelcoefficients between the transmitting terminal 230 and the receivingterminals 240 and 220, respectively.

It will be understood that the interference between communications isrepresented in (1) by the crossed terms.

For the first communication, the respective powers of the informationand interference signal due to the second communication are respectively|g₁₁|²P₁ and |g₁₂|²P₂.

It will be noted that this model is similar to the traditional two-usermulti-access channel model called MAC (Multiple Access Channel) as forexample described in the article by Shih-Chun Chang et al. entitled“Coding for T-User Multiple-Access Channels,” IEEE Transactions onInformation Theory, vol. IT-25, no. 6, pp. 684-691, November 1979.

It fundamentally differs from the aforementioned article, however,inasmuch as in the MAC model, the receiving terminals receive usefulinformation and not interference information on the “crossed” channels.

The signal to noise ratio (SNR) at the first receiver can be expressedin the form:

$\begin{matrix}{\gamma_{1} = {{g_{11}}^{2}\frac{P_{1}}{N_{0}}}} & (2)\end{matrix}$

Similarly, the interference to noise ratio at the first receiver is noneother than:

$\begin{matrix}{\delta_{1} = {{g_{12}}^{2}\frac{P_{2}}{N_{0}}}} & (3)\end{matrix}$

Likewise, the signal to noise and interference to noise ratios at thesecond receiver can respectively be written as:

$\begin{matrix}{\gamma_{2} = {{g_{22}}^{2}\frac{P_{2}}{N_{0}}}} & (4) \\{\delta_{2} = {{g_{21}}^{2}\frac{P_{1}}{N_{0}}}} & (5)\end{matrix}$

It will be noted that the following relationships are verified:

$\begin{matrix}{{\delta_{1} = {{f_{2}\gamma_{2}\mspace{14mu} {and}\mspace{14mu} \delta_{2}} = {f_{1}\gamma_{1}}}}{where}} & (6) \\{f_{1} = {{\frac{{g_{21}}^{2}}{{g_{11}}^{2}}\mspace{14mu} {and}\mspace{14mu} f_{2}} = {\frac{{g_{12}}^{2}}{{g_{22}}^{2}}.}}} & \left( 6^{\prime} \right)\end{matrix}$

Hereinafter ρ₁ and ρ₂ will denote the respective rates on the first andsecond communications and the variables C₁=2^(ρ) ¹ −1, C₂=2^(ρ) ² =1 andC₁₂=2^(ρ) ¹ ^(+ρ) ² −1 are introduced.

For a given pair of rates (ρ₁,ρ₂), it is possible to distinguish severalinterference regimes, each regime giving rise to separate processing.More precisely, if one considers the first communication, it is possibleto classify the interference in three possible regimes:

Diagrammatically, in a first regime, the power of the interference dueto the second communication is lower than the power of the informationsignal received at the first receiving terminal. More precisely, if onereasons in terms of capacity within the meaning of Shannon, the signalto noise plus interference ratio on the direct channel between thetransmitting terminal 210 and the receiving terminal 220 makes itpossible to pass the rate ρ₁ whereas the signal to noise ratio on the“crossed” channel between the transmitting terminal 230 and thereceiving terminal 220 does not make it possible to pass the rate ρ₂(the “crossed” channel is in a cutoff situation within the meaning ofthe information theory), in other words:

$\begin{matrix}{{\rho_{1} \leq {\log_{2}\left( {1 + {SINR}_{11}} \right)}} = {\log_{2}\left( {1 + \frac{\gamma_{1}}{1 + \delta_{1}}} \right)}} & (7)\end{matrix}$

and

ρ₂>log₂(1+INR ₁₂)=log₂(1+δ₁)   (8)

where SINR₁₁ and NR₁₂ are respectively the signal to noise plusinterference ratio and the interference to noise ratio at the firstreceiving terminal.

In this regime, the information signal of the second communicationcannot be decoded due to the cutoff of the crossed channel. It is thenconsidered thermal noise for decoding the information signal of thefirst communication.

The stresses on δ₁ and γ₁ relative to the first regime are deduced from(7) and (8):

γ₁ ≧C ₁(1+δ₁)   (9)

γ₁<C₂   (2)

Conversely, in a third regime, the power of the interference issubstantially greater than that of the information signal received bythe first receiving terminal. Given that the interference is due to thesecond communication, it is proposed to first decode the informationsignal of the second communication, to estimate the interference due tothis communication, and to subtract it from the received signal. Theinformation signal of the first communication is then decoded from theresulting signal, rid of the interference.

In this regime, in a first step one considers the signal from the firstcommunication as thermal noise and decodes the information signal of thesecond communication. One is therefore in a situation symmetrical tothat of the first regime and expression (7) is replaced by:

$\begin{matrix}{{\rho_{2} \leq {\log_{2}\left( {1 + {SINR}_{12}} \right)}} = {\log_{2}\left( {1 + \frac{\delta_{1}}{1 + \gamma_{1}}} \right)}} & (11)\end{matrix}$

where SINR₁₂ is the “signal to noise” ratio at the receiving terminal220 in which the signal is heard as the information signal of the secondcommunication.

In a second step, once the contribution of the second communication issubtracted from the received signal, one is in the case of a signalsimply noised by a thermal noise, in other words:

ρ₁≦log₂(1+SNR ₁₁)=log₂(1+γ₁)   (12)

where SNR₁₁ is the signal to noise ratio after elimination of theinterference due to the second communication.

Expressions (11) and (12) translate to the following stresses on γ₁ andδ₁:

$\begin{matrix}{\gamma_{1} \leq {\frac{\delta_{1}}{C_{2}} - 1}} & (13)\end{matrix}$

and

γ₁≧C₁   (14)

Lastly, in a second regime, the power of the interference is of the sameorder as that of the information signal. It is then proposed to jointlydecode the information signal of the first communication and theinformation signal of the second communication at the first receivingterminal. The joint decoding of the two information signals may, forexample, be done using a PIC system or a maximum likelihood decodingmethod of the MMSE-GDFE (Minimum Mean Square Error-Generalized DecisionFeedback Equalizer) type, in a known manner.

This interference regime is intermediate between the first and thirdinasmuch as the rate ρ₂ no longer verifies (8) and (11), in other words:

$\begin{matrix}{{\log_{2}\left( {1 + \frac{\delta_{1}}{1 + \gamma_{1}}} \right)} < \rho_{2} \leq {\log_{2}\left( {1 + \delta_{1}} \right)}} & (15)\end{matrix}$

However, the joint decoding assumes that the rates of the first andsecond communications can be conveyed by the channel made up of thedirect channel and the crossed channel, i.e.:

ρ₁+ρ₂≦log₂(1+γ₁+δ₁)   (16)

The stresses on γ₁ and δ₁, relative to the second regime, are deducedfrom (15) and (16):

C ₂≦δ₁ <C ₂(1+γ₁)   (17)

and

γ₁ ≧C ₁₂−δ₁   (18)

FIG. 3 shows an interference diagram in which the x-axis shows theinterference to noise ratio δ₁ and the y-axis shows the power to noiseratio γ₁.

This diagram is obtained for given rate values ρ₁ and μ₂, and as aresult for the given values of C₁, C₂, C₁₂ .

The ratio γ₁ varies from 0 to γ₁ ^(max)=|g₁₁|²P₁ ^(max)/N₀ and the ratioδ₁ varies from 0 to δ₁ ^(max)=|g₁₂|²P₂ ^(max)/N₀ where P₁ ^(max) and P₂^(max) are respectively the maximum transmission powers of the terminals210 and 230.

The lines A₁ and A₂ defined by the equations δ₁=C₂ (cf. (10)) and

$\gamma_{1} = {\frac{\delta_{1}}{C_{2}} - {1\mspace{14mu} \left( {{cf}.\mspace{14mu} (13)} \right)}}$

delimit the three interference regimes. The lines D₁, D₂, D₃,respectively defined by the equations γ₁=C₁(1+δ₁) (cf. (9)); γ₁=C₁₂—δ₁(cf. (18)); γ₁=C₁ (cf. (14)) ; give the lower power border, noted Λ, foreach of these regimes. The zone 310 corresponding to the firstinterference regime is delimited by the lines D₁ and Δ₁ as well as theordinate axis, that corresponding to the second interference regime,320, is delimited by the lines Δ₁, Δ₂ and D₂, and lastly that 330corresponding to the third interference regime is delimited by Δ₂ andD₃.

Below the lower border Λ is a fourth zone 340 in which it is notpossible to process the interference for the requested service quality,here for the rates ρ₁ and ρ₂. It may then be possible to use anotherradio resource, for example another transmission time interval toeliminate the interference between the two communications.

If the rate of the first or second communication varies, the parametersof the equations of the lines D₁, D₂, D₃ and Δ₁, Δ₂ also vary and, as aresult, the zones corresponding to the different interference regimesare modified.

For the given rates ρ₁ and ρ₂, it is possible to determine, from anestimate, at the receiver, the power of the information signal, thepower of the interference and that of the thermal noise, in whichinterference regime one is located, and to perform the processingrelated to said zone.

Moreover, as indicated in the figure, for given rates ρ₁ and ρ₂, it ispossible to determine, for each interference power δ₁, the lowest valueof designated here by γ₁*, making it possible to process saidinterference. In other words, for a given transmission power of theterminal 230, it is possible to allocate the minimum power

$P_{1}^{*} = {\frac{N_{0}}{{g_{11}}^{2}}{\gamma_{1}^{*}.}}$

to the transmitting terminal 210. It will be noted that if one is in thezone 320 or 330, this allocated power value is much lower than that,designated here by γ₁ ^(th), that it would have been necessary toallocate if one had likened the interference to simple thermal noise.

FIG. 4 shows an interference diagram in which this time the x-axis showsthe power to noise ratio γ₂ and the y-axis shows the power to noiseratio γ₁.

The ratio γ₁ varies from 0 to γ₁ ^(max)=|g₁₁|²P₁ ^(max)/N₀ and the ratioγ₂ varies from 0 to γ₂ ^(max)=|g₂₂|²P₂ ^(max)/N₀.

Inequalities (9), (13) and (18) can be rewritten as a function of theratios γ₁ and γ₂, using (6):

$\begin{matrix}{\gamma_{1} \geq {C_{1}\left( {1 + {f_{2}\gamma_{2}}} \right)}} & (19) \\{\gamma_{1} \leq {{\frac{f_{2}}{C_{2}}\gamma_{2}} - 1}} & (20) \\{\gamma_{1} \geq {C_{12} - {f_{2}\gamma_{2}}}} & (21)\end{matrix}$

Similarly to FIG. 3, the lines Δ₁ and Δ₂ defined by the equationsγ₇₂=C₂/ƒ₂ (cf. (10)) and

$\begin{matrix}{\gamma_{1} = {{\frac{f_{2}}{C_{2}}\gamma_{2}} - {1\mspace{14mu} \left( {{cf}.\mspace{14mu} (20)} \right)}}} & \;\end{matrix}$

delimit the three interference regimes and the lines D₁, D₂, D₃,respectively defined by the equations γ₁=C₁(1+ƒ₂γ₂) (cf. (19));γ₁=C₁₂−ƒ₂γ₂ (cf (21)); γ₁=C₁ (cf. (14)); provide the lower powerboundary Λ. The zones corresponding to the different interferenceregimes are designated by 410, 420 and 430.

FIG. 5 shows an interference diagram identical to that of FIG. 4 inwhich the different interference regimes are indicated for bothcommunications. The signal to noise ratio γ₁ is shown on the x-axis andthe signal to noise ratio γ₂ on the y-axis. Nine distinct zones areobtained by the intersection of three zones relative to the firstcommunication and three zones relative to the second communication.These nine zones are denoted Ω_(pq), 1≦p≦3, 1≦q≦3, where p and qrespectively index the interference regime of the first and secondcommunications. The different zones are delimited by the lines Δ¹ ₁,Δ¹₂,Δ² ₁,Δ² ₂, D₁ ¹,D₂ ¹,D₃ ¹, and D₁ ²,D₂ ²,D₃ ² where the upper indexhere indicates the communication.

The lower borders Λ₁ and 79 ₂ relative to the two communicationsintersect at a point Γ′=(γ₁*,γ₂*). For given communication rates ρ₁ andρ₂, the point Γ* corresponds to the minimum power allocation. Ingeneral, the zone Ω_(p)*_(q)* in which the point Γ* is located providesthe interference regimes p*,q* for the two communications and as aresult the types of processing to be done at the corresponding receivingterminals. It will be noted that in the illustrated case, it is the zoneΩ₂₁ that contains the operating point, in other words for decoding theinformation signal of the first communication, one will proceed with ajoint decoding (at the first receiving terminal), and for decoding theinformation signal of the second communication (at the second receivingterminal), the first communication will be likened to thermal noise.

Conversely, for given transmission powers, it is possible to determinethe maximum rates ρ₁* and ρ₂*

allowing the interference processing. In fact, this amounts to lookingfor the couple of lower boundaries Λ₁* and Λ₂* whereof the pointΓ=(γ₁*,γ₂*) is the intersection. The zone where the point γ=(γ₁*,γ₂*) islocated also provides the types of interference processing as previouslydescribed.

More generally, for given transmission powers, it is possible to seek tooptimize a function of interest ƒ(ρ₁,ρ₂), jointly depending on the ratesof the first and second communications. For example, it is possible toseek to maximize the sum of the rates (Sum Rate Scheduling) or toguarantee a minimum rate (Min Rate Scheduling) or rates proportional tothe connection quality (Fair Rate Scheduling).

Lastly, it will be understood that other functions of interest could beoptimized similarly from the interference diagram. The function ofinterest in question may in particular depend on other service qualityparameters such as the latency time on communications or the spatialcoverage of the terminals.

Whatever the form, the maximization of the function of interest on theinterference diagram, for given transmission powers, makes it possibleto obtain the optimal values of the service quality parameters.

FIG. 6 diagrammatically illustrates a flowchart of the communicationmethod according to one embodiment of the invention.

This embodiment assumes that two couples of transmitting and receivingterminals of the wireless telecommunications system have previously beenselected because their communications use the same radio resources andinterfere with each other (intra-band interference).

In step 610, the channel coefficients g_(mn), m=1,2 are estimated;n=1,2; between the transmitting terminals and the receiving terminals,for example using pilot symbols, in a known manner.

In step 620, for a transmission power range [P₁ ^(min), P₁ ^(max)] ofthe first transmitting terminal, a transmission power range [P₂ ^(min),P₂ ^(max)] of the second transmitting terminal, and at least one pair ofrate values of the first and second communications, an interferencediagram (δ₁,γ₁) or (γ₂,γ₁) is determined from the previously estimatedcoefficients, ĝ_(mn), for at least the first communication or even forboth communications.

In step 630, one determines, for at least the first communication, apartition of the interference diagram into a plurality of separatezones. An interference processing is associated with each of thesezones.

Advantageously, the partition will be used in three zones, as previouslydescribed.

In the first zone, the interference due to the second communication isof low power relative to the information signal of the firstcommunication. The interference is then processed as thermal noise fordecoding this information signal.

In the second zone, the interference due to the second communication isof the same power order as the information signal of the firstcommunication. One then proceeds with joint decoding of the informationsignals of the two communications.

Lastly, in a third regime, the interference due to the secondcommunication has a power substantially greater than that of theinformation signal of the first communication. The information signal ofthe second communication of the received signal is then first decoded,said interference is estimated from the signal thus decoded (and thechannel coefficient g₁₂). The estimated interference is subtracted fromthe received signal to generate a signal rid of interference. Lastly,the information signal of the first communication is decoded from thelatter signal.

As indicated above, it is possible to proceed with a partition of theinterference diagram both for the first and second communications.Generally, one then obtains a partition in P² distinct zones Ω_(ij)where P is the number of interference regimes for a singlecommunication.

In practice, the different zones are delimited by the lines Δ^(k) _(q)and D_(s) ^(k), q=1,2, s=1,2,3 where k=1,2 is the index of thecommunication.

In step 640, the zone is selected where the operating point of the firstreceiving terminal is found, for example given by the signal to noiseand interference to noise ratio at that terminal.

This operating point can be obtained in different ways.

First, it can be determined by the receiving terminal from an estimateof the respective powers of the information signal, the interference andthe thermal noise. These powers can for example be obtained by providingperiods of silence in the first and second communications, the thermalnoise being measured during a period of silence for the twocommunications. The thermal noise can also be measured using sequencesof pilot symbols.

Alternatively, the operating point can be provided directly by a powerreference for the transmitting terminals. The powers of the informationand interference signal, at the receiving terminal, are then calculatedfrom the channel coefficients.

The operating point can also be determined using a minimum powerallocation method. In that case, the allocated powers are obtained bythe intersection of the curves Λ₁ and Λ₂, as seen above.

Reciprocally, for a given operating point Γ, it is possible to look forthe rates ρ₁*,ρ₂* maximizing a utility function ƒ(ρ₁,ρ₂) at theoperating point. The rates ρ₁*,ρ₂* then determine a partition of theinterference diagram, since the equations of the lines Δ_(q) ^(k) andD_(s) ^(k) depend on them.

In step 650, the zone thus selected is used to deduce the type ofprocessing of the interference (i,j) to be done at the first and/orsecond receiver(s) and the processing is done in the receiver dependingon the selected type.

The communication method according to the invention is generalized toany number K of pairs of terminals and therefore a number K ofcorresponding communications. The interference diagram of FIG. 4 or 5 isthen built in a space with K≧2 dimensions and one has P^(K) possiblecombinations of P interference regimes for the set of K communicationsof the system.

Since this number can be very high, one can opt for a sub-optimalsolution that is easier to implement.

According to this solution, the couples of transmitting and receivingterminals T=(E_(k),R_(k)), k=1, . . . , K are selected one by one whereE_(k) is a transmitting terminal in communication with a receivingterminal R_(k). For a couple T_(k), one looks for the couple T_(k′)whereof the communication k′ causes the strongest level of interferenceon the communication k. One then groups T_(k) and T_(k′) in the form ofa pair. The method continues with the remaining terminals until all ofthe couples T_(k) are paired up, with the exception of one if K is odd.

Advantageously for a given couple T_(k), the search for the coupleT_(k′) causing the high level of interference can be done by comparingthe channel coefficient ratios

${\overset{\sim}{f}}_{k}^{k^{\prime}} = \frac{g_{{kk}^{\prime}}}{g_{kk}}$

where g_(kk′) is the coefficient of the “crossed” channel between E_(k′)and R_(k) and g_(kk) is the coefficient of the direct channel betweenE_(k) and R_(k). The selected couple T^(k′) is that corresponding to thehighest ratio f_(k) ^(k′).

For a pair (T_(k),T_(k′)) thus formed, it is possible to consider thatthe other pairs are only slightly interfering. The “residual”interference due to the other communications will be processed asthermal noise and consequently will not influence the choice of the typeof processing of the interference for the communication k.

Once the interference diagram is determined for the pair (T_(k),T_(k′))and the zones of the different identified interference regimes, aminimum power allocation can be done complying with a stress on therates ρ_(k) and ρ_(k′) (and generally on a service quality metric). Itis then possible for the powers allocated to the different transmissionterminals to modify the interference system. In this case, it ispossible to iterate the process for grouping couples into pairs,determining the interference and minimum power allocation zones, untilone converges or a maximum number of iterations is reached. Theconvergence can for example be verified by comparing, relative to athreshold, the sum of the deviations between successive powerscalculated over all of the transmitting terminals. The convergencecriterion can be assessed for all of the pairs or independently, pair bypair.

In any case, after the pairs (T_(k),T_(k′)) have been formed, the powerdiagrams are calculated for each of these pairs and the interferencezone are identified in each of these diagrams. This operation can bedone in a centralized manner by a dedicated node or distributed in thereceiving terminals.

In any case, one skilled in the art will understand that the calculationcan be done using a microprocessor, a specialized mathematical processor(DSP) or by reading in a ROM in which calculating results havepreviously been stored (look-up table).

1. A communication method for a cellular telecommunications systemcomprising at least one first couple of terminals formed by a firsttransmitting terminal and a first receiving terminal and a second coupleof terminals formed by a second transmitting terminal and a secondreceiving terminal, a first communication between the terminals of thefirst couple using the same radio resources as a second communicationbetween the terminals of the second couple, such that the twocommunications interfere with each other, characterized in that: thechannel coefficients are estimated (610) between said transmittingterminals and said receiving terminals; an interference diagram isdeduced (620) for at least the first receiving terminal, the diagrambeing obtained for a first transmission power range of the firsttransmitting terminal and a second transmission power range of thesecond terminal, and for at least one couple of rates for the first andsecond communications; for the considered couple of rates, a partitionof the diagram into different zones is determined (630), each zonecorresponding to a distinct type of processing of the interference forat least the first communication; a zone of the partition is selected(640) containing an operating point of the first and second receivingterminals; at least in the first receiving terminal, the processing isdone (650) for the interference corresponding to the zone thus selected.2. The communication method according to claim 1, characterized in thatin the first type of processing, the interference is processed asthermal noise to decode said information signal of the firstcommunication.
 3. The communication method according to claim 1,characterized in that in the second type of processing, the informationsignals of the first and second communications are the subject of jointdecoding.
 4. The communication method according to claim 1,characterized in that in the third type of processing, the informationsignal of the second signal is first decoded, an estimate of theinterference signal due to the second communication is deduced therefromand it is subtracted from the signal received by the first receiver, theinformation signal of the first communication being decoded from thesignal thus obtained.
 5. The communication method according to one ofthe preceding claims, characterized in that said operating point isobtained by minimizing the power allocated to the first transmittingterminal for a given rate of the first communication.
 6. Thecommunication method according to one of claims 1 to 4, characterized inthat said operating point is obtained by joint minimization of thepowers respectively allocated to the first and second transmittingterminals, under a stress pertaining to a first service quality metric.7. The communication method according to claim 6, characterized in thatsaid operating point is obtained by joint minimization of the powersrespectively allocated to the first and second transmitting terminalsfor given rates of the first and second communications.
 8. Thecommunication method according to one of claims 1 to 4, characterized inthat a plurality of partitions is determined and that zone is obtainedby selecting the one of said partitions maximizing, at the operatingpoint, a utility function depending on the rate of the firstcommunication.
 9. The communication method according to one of claims 1to 4, characterized in that a plurality of partitions is determined andthat zone is obtained by selecting the one of said partitionsmaximizing, at the operating point, a utility function jointly dependingon the respective rates of the first and second communications.
 10. Thecommunication method according to claim 9, characterized in that saidutility function is the sum of the rates of the first and secondcommunications.
 11. The communication method according to claim 9,characterized in that said utility function is a minimum rate for thefirst and second communications.
 12. The communication method accordingto one of the preceding claims, characterized in that said communicationsystem comprises a plurality of couples each formed by a transmittingterminal in communication with a receiving terminal and in that thecouples are grouped together in pairs by selecting, for each firstcouple of terminals, a second couple of terminals of said pluralitygenerating the strongest interference level on the communication betweenthe terminals of the first couple, the first couple of terminals and thesecond couple of terminals then constituting a pair.